The concept comes from Hermann Usener in Gotternamen, in Bonn, 1896 in German, later translated into English.(1)
momentary god (plural momentary gods)
- A deity who exists for a specific purpose, and at a specific time at a special place. It has no existence except for such purpose, time, and place.(1)
Clear examples are the Greek figures of Euodos, Horophylax, and Myiagros, who chased away the flies during the sacrifices to Zeus and Athena.
(1) Hastings, James. Momentary Gods, in Encyclopedia of Religion and Ethics, Part 16. Kessinger Publishing, 2003. Pages 777-778. ISBN 0766136930.